Try N&C in new Brighton used to do stuff with them a while back or MES in deeside although they are big into Jet Ski's

Failing that give me a shout and i can put you onto the engineer who used to service all our inboards and outboards from Yammaha to Mastercraft Corvette LT1 engines He does bikes aswell and has opened up a unit in Hoylake BM Wirral - not like alot of the unprofessional clowns you come across